I have often read that logical positivism holds only empirical data to be valid, yet as this view can't be empirical confirmed, it refutes itself. Is this true?
MAGEE: Now logical positivism must have had actually some real defects. What do you now in retrospect think the main shortcomings of the movement were.
AYER: I suppose the greatest defect...is that nearly all of it was false. (hearty laughter from the two of them)
MAGEE: I think you need to say a little more about that.
AYER: Perhaps that’s being too harsh on it. I still want to say that it was true in spirit in a way, that the attitude was right. But if one goes for the details, first of all the verification principle never got itself properly formulated. I tried several times and it always let in either too little or too much, and to this day it hasn’t received a properly logically precise formulation. Then, the reductionism just doesn’t work. You can’t reduce statements, even ordinary simple statements about cigarette cases and glasses and ashtrays, to statements about sense data, let alone more abstract statements of science...If you go in detail very, very little survives. What survives is the general rightness of the approach.
You might enjoy David Rynin's 1956 address to the American Philosophical Association, "Vindication of L*G*C*L P*S*T*V*SM":
I pointed out at the beginning that to vindicate a position is not the same as to show that it is perfect, and we see the kind of imperfection that remains. It strikes me as minute enough so that one can with some justification adopt the Verifiability principle with a minimum of sacrifice of sentences that might be thought to be cognitively meaningful. To weaken it so as to include the relevant cases of mixed quantification is to introduce an extremely unclear notion of confirmation, one that seems of little if any use in the pursuit of knowledge. But if one chooses to weaken it in the manner indicated we are still left with a conception in some sense resting on the notion of truth conditions or something very much like it; and I daresay that most of those who object to the stronger version of the principle would not be very much more content with the weaker. ...
It is worth pointing out that the only prominent thinker committed to the Verifiability principle who was interested enough in ethics to bother to write a book on the subject, Moritz Schlick, emphatically did not treat ethical statements as meaningless, and on the subject of metaphysics wrote the following: "If one wishes to characterize every view which denies the possibility of metaphysics as positivistic this is quite unobjectionable, as a mere definition; and I should in this sense call myself a strict positivist. But this holds, of course, only under the presupposition of a special definition of 'metaphysics.'" (And concerning that special definition, he wrote "...it hardly agrees with the formulations usual in philosophic literature...") It was in fact a definition according to which metaphysical statements attempt to express what is not, in his sense, expressible, i.e. content.
If to be a logical positivist is to be one who adopts the Verifiability principle for use in dealing with the problem of the meaning and meaningfulness of statements as they function within the context of cognition then I am prepared to call myself one; but if it be to be one characterized by the above mentioned bad logic and worse manners I wish not to be called one. ...
It is often thought that the Verifiability principle is somehow especially wedded to sense data, that according to it only statements verifiable and falsifiable, or perhaps confirmable, in terms of the data of one or more of the five senses are meaningful. But this is surely not essential. How many senses there are and what constitute the data of sense are themselves not very well formulated question, and it would be much more illuminating I believe to define "the given" in terms of "ascertainable truth conditions" than the latter in terms of the former. Truth is our goal. What difference does it make in what form or what materials ascertainment comes to us, so long as it comes? It is certainly in some sense correct that all ascertainment comes to us through the confrontation of data of some kind; but let not the paucity of language blind us to the fact that there is more under heaven than is dreamt of in our vocabularies.
It is a misrepresentation to characterize logical positivism as only holding "empirical data to be valid." Logical positivism just holds that philosophy should aspire to the same sort of rigor as science.
We are like sailors who on the open sea must reconstruct their ship but are never able to start afresh from the bottom. Where a beam is taken away a new one must at once be put there, and for this the rest of the ship is used as support. In this way, by using the old beams and driftwood the ship can be shaped entirely anew, but only by gradual reconstruction.
-Otto Neurath (1921)
Logical positivism is sort of self contradictory in a different way. It rejects assumptions about the existence of an underlying (observer independent objective) reality, but uncritically accepts the existence of empirical data. But often empirical data can only be collected, if there is at least some theory of an underlying reality. It is a bit like saying "the statistics says ..." without realising how much what the statistics say is influenced by how you asked the questions and how you interpreted the answers.
Edit Maybe the downvote is justified. I now tried to track down references for the critique of logical positivism expressed above. So far, the best source seems to be the critique of Ernst Mach's idea that a physical theory should only contain quantities which can be observed. The problem here is that it is unclear to which extend logical positivism subscribes to Ernst Mach's idea. Werner Heisenberg was confronted with that critique in 1926 by Albert Einstein (see Werner Heisenberg "Der Teil und das Ganze" Kapitel 5), but that doesn't mean that Einstein is the original author of that critique. Interestingly enough though, that critique cannot be applied to the original Copenhagen interpretation of quantum mechanics, since it explicitly accepts and uses classical physics as the mean to describe observations, i.e. empirical data. (Not sure whether this means that the original Copenhagen interpretation is not positivistic.)